A 5600-YEAR RECORD OF PALEOHYDROCLIMATE FROM LOWER PAHRANAGAT LAKE, SOUTHERN GREAT BASIN

Continuous, high-resolution archives of paleoclimate are rare for the arid Great Basin province of the United States. Such records provide valuable paleoclimate context for a region of the United States that is especially fast-growing and drought-prone in the midst of rapid climate change. Here, we present a 5600-year sediment core-based record of hydroclimate spanning the later mid-Holocene to recent from Lower Pahranagat Lake (LPAH) in southern Nevada. LPAH is a shallow, spring-fed, alkaline lake and our 13.2 m – long sequence of overlapping cores is dominated by Mg carbonate-rich muds (carbonate typically 50-80%) with evidence of microbial-influenced carbonate precipitation. We extend and build on our earlier core-based work on LPAH (Hickson et al., 2016), applying stable isotopic values (δ¹⁸O and δ¹³C) from downcore fine-fraction (<63 µm) carbonates which are sensitive to hydroclimate in this highly evaporative region. Additional geochemical proxies (TOC/TN/C:N, %CaCO₃, and XRD data) provide supporting information on regional hydroclimate and paleoecological change in and around the lake. Numerous records from across the Great Basin have established the Middle Holocene (~7000 – 4000 years B.P.) as a warmer and drier period than the Late Holocene for this region. Especially low δ¹⁸O values and a sharp facies change from a peat layer to carbonate mud near the base of the LPAH core record ¹⁴C age-dated to ~4800 yrs BP signals a shift to wetter conditions at the latter part of the Middle Holocene and the filling of the lake. Following this, our geochemical data suggest a series of century-scale fluctuations in the hydroclimate of the region. We compare and contrast our record with others from the Great Basin with special emphasis on the high-resolution Leviathan Cave stalagmite record (Lachniet et al., 2014) collected near LPAH. We evaluate the significance of Pacific Ocean SSTs and other relevant forcings to the LPAH record of paleohydroclimate.